A vehicle such as a truck, a bus, or a construction machine controls the systems of brakes, suspensions, and the like using compressed air delivered by a compressor, which is directly connected to the engine. The compressed air contains water contained in the atmospheric air and oil for lubricating the interior of the compressor. If the compressed air containing the water and the oil enters the systems, metal rusting and swelling of rubber members (such as O-rings) occur, thus causing malfunction. Therefore, an air drier, which removes water and oil from compressed air, is arranged downstream of the compressor in an air system (see, for example, Patent Document 1).
The interior of the air drier is filled with a filter and desiccant such as silica gel and zeolite. The air drier removes water from the compressed air to dry the compressed air by the desiccant adsorbing the water.
During a loading operation (dehumidifying operation) which removes water, the air drier causes compressed air delivered through the inlet to pass through the drying container and supplies the air to an air tank through an outlet while retaining the compressed dry air in a case of the air drier. During an unloading operation (regenerating operation) which regenerates the desiccant, the air drier opens an exhaust valve of a collected liquid discharging device to cause the compressed dry air retained in the case of the air drier to pass through the drying container and discharge purge air, which contains oil and water, through a collected liquid discharge port. The air drier periodically repeats the loading operation and the unloading operation.
In regeneration of the desiccant of the air drier, purge air discharged from the air drier contains oil as well as water. Thus, considering the environmental burden, providing an oil separator downstream of the collected liquid discharge port in the air drier has been proposed (see, for example, Patent Document 2). In the oil separator, an impingement member is provided in a housing for purge air containing oil and water to strike. The oil separator performs vapor-liquid separation by causing the purge air to strike the impingement member to collect oil and water and discharge clean air.